Rotary lawn mower cutting blade

ABSTRACT

A rotary lawn mower cutting blade with reduced drag and improved cutting ability includes a central mounting section, intermediate sections, and outboard sections along a common longitudinal axis and disposed about a common center of rotation. The outboard sections include downward and inward projecting sections. The cutting blade also preferably includes cutting edges on the full extent of the leading edge of the outboard section including the downward and inward projecting sections. Additionally, the outer section can be twisted slightly to enhance airflow upward.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 11/706,165 filed Feb. 15, 2007 entitled, “Rotary Lawn Mower Cutting Blade.” The above application is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cutting blade for rotary lawn mowers.

2. Prior Art

Conventional rotary lawn mower cutting blades are made of an elongated flat metal plate, rectangular in shape, with a central mounting portion and an outer portion having a leading beveled cutting edge, and a bend or twist of either the entire outer portion of the blade or just the trailing edge of the outer portion to generate airflow used to draw the uncut grass upward into the path of the cutting edge and to expel the cuttings from the cutting area. Raised teeth may be added to the trailing edge of the outer portion of the blade to produce a mulching action.

The problem with present art rotary lawn mower cutting blades is that the central mounting portion is generally in the same plane as the cutting portion, resulting in lost energy as the central mounting portion passes over and impinges upon the top edge of the cut grass and residual clippings. Energy is wasted, efficiency of the lawn mower is impaired, and airflow through the cutting area is restricted.

It is the object of this invention to provide a novel rotary lawn mower cutting blade which has improved cutting abilities and can operate with greater efficiency.

BRIEF SUMMARY OF THE INVENTION

According to the invention, a rotary lawn mower cutting blade which provides for improved cutting action with greater efficiency, comprises a central mounting portion, two oppositely extending intermediate portions connecting to outer portions which are in turn joined to downward-turned end portions which are in turn joined to inward turned cutting portions.

According to the invention, the downward-turned end portions may be straight or curved and may be directed downward in a perpendicular orientation from the plane of the central mounting portion, or at some obtuse or acute angle therefrom. The downward-turned end portion may also be skewed to the axis of rotation of the cutting blade, which places the leading edge of the end portion at a greater or less distance from the center of rotation than the trailing edge.

According to the invention, airflow can be enhanced during rotation of the blade by applying a slight twist to the intermediate or outer portion of the blade, the trailing edge of the outer portion, the trailing edge of the cutting portion, or some combination thereof .

BRIEF SUMMARY OF THE SEVERAL VIEWS OF THE DRAWING

Reference will be made to the preferred embodiment, examples of which are illustrated in the accompanying drawing figures. The figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of this preferred embodiment, it should be understood that it is not intended to limit the scope of the invention to this particular embodiment.

Certain elements in selected views of the drawings may be illustrated not-to-scale, for illustrative clarity. Elements of the figures can be numbered such that similar (including identical) elements may be referred to with similar numbers in a single drawing. Such relationships, if any, between similar elements in the same or different figures will become apparent throughout the specification, including, if applicable, in the claims and abstract.

The structure, operation, and advantages of the present preferred embodiment of the invention will become further apparent upon consideration of the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a first embodiment of a rotary lawn mower cutting blade according to the present invention;

FIG. 2 is a partial perspective view of the outer portion 8 of the cutting blade shown in FIG. 1;

FIG. 3 is a perspective view of a second embodiment of a rotary lawn mower cutting blade according to the present invention;

FIG. 4 is a partial perspective view of the outer portion 8 of the cutting blade shown in FIG. 3. Areas in the respective foregrounds of FIGS. 1-4 can be regarded as areas forward of the illustrated cutting blade. Areas in the respective background of FIGS. 1-4 can be regarded as areas rearward of the illustrated cutting blade.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 and FIG. 2, there is shown a rotary mower cutting blade 101 that is an embodiment of the present invention having a central portion 2 which includes a central bore 1 for attaching blade 101 to a source of rotating power. The cutting blade is further provided with outer portions 7 which are joined to the central portion 2 by intermediate portions 8 along a common longitudinal blade axis. The cutting portions 10, which have leading cutting edges 6 and trailing edges 5, are joined to the outer portions 7 through the downward portions 9. The outer portion 7 has a trailing edge 3 and the downward portion 9 has a trailing edge 4. As seen in FIG. 1, the central portions, intermediate portions, and outer portions can be generally planar and can be disposed generally in a common plane. The leading cutting edges 6 of the cutting portions 10, which are beveled from the inner surface of the cutting portion 10 downward in this embodiment, are continued through the downward portions 9 where the bevel direction becomes outward and outer portions 7 where the bevel direction becomes upward, however it of course may be understood that the direction of bevel and portions of the blade which are beveled to form a cutting edge can vary.

In this embodiment, the cutting blade is twisted slightly in the intermediate portion 8. This will facilitate directing air upward during rotation of the cutting blade as air is directed upward along the surface of the outer portion 7 and the cutting portion 10. As an alternative, trailing edge 5 and/or trailing edge 3 can be bent or twisted upward to create upward airflow during rotation of the cutting blade, and can also be formed into teeth as in U.S. Pat. No. 6,487,840 to create a mulching action of the grass clippings.

In this embodiment, the plane of the downward portions 9 are perpendicular to the plane of the central portion 2, however this angular relationship may be acute or obtuse. Therefore, where in this specification and claims I employ the term “downward”, I intend an angular relationship which will result in a general downward projection. The plane of the downward portion 9 can also be skewed or twisted in the vertical plane so as to cause the trailing edge 4 to be further away from the center of rotation of the cutting blade than any other point on the surface of the downward portion 9. This vertical twist will result in airflow being directed outward during rotation of the cutting blade which will improve removal of the grass clippings from the cutting area.

FIG. 3 and FIG. 4 illustrates a cutting blade 201 that is a second preferred embodiment of the invention. The cutting blade 201 is substantially identical to cutting blade 101, with the exception that the downward portion 9 is curved rather than straight. Edge 11 that is shown as being intermediate of edge 5 and edge 6 and which is labeled in FIGS. 2 and 4 and shown through the views can be regarded as an interior edge of the respective cutting portion on which it is included. As shown in FIGS. 1 and 3, an interior edge of a first cutting portion can generally face an interior edge of a second cutting portion.

Compared to prior art designs, the present invention provides a cutting blade with improved energy efficiency by moving the central mounting portion and intermediate portions well above the cutting surface, improved cutting action by providing for multiple cutting edges, and a cutting blade which is economical to produce.

While this invention has been described in the specification and illustrated in the drawings with respect to a preferred embodiment, it is understood that all changes and modifications that come within the spirit of the invention are desired to be protected. Undoubtedly, many variations or equivalents may be substituted for elements of the invention by one having ordinary skill in the art to which the present invention most nearly pertains, and such variations are intended to be within the scope of the invention, as disclosed herein; 

1. A rotary lawn mower cutting blade comprising: a center portion joined to respective intermediate portions which in turn are joined to respective first and second outer portions; first and second inwardly extending cutting portions, the first inwardly extending cutting portion being joined to said first outer portion through a first downwardly extending end portion extending downwardly from said first outer portion, the second inwardly extending cutting portion being joined to said second outer portion through a second downwardly extending end portion extending downwardly from said second outer portion; wherein said first cutting portion has an inwardly extending leading cutting edge and an inwardly extending trailing edge, the leading cutting edge of said first cutting portion facing forward of said rotary lawn mower cutting blade, the trailing edge of said first cutting portion facing rearward of said rotary lawn mower cutting blade; and wherein said second cutting portion has an inwardly extending leading cutting edge and an inwardly extending trailing edge, the leading cutting edge of said second cutting portion facing rearward of said rotary lawn mower cutting blade, the trailing edge of said second cutting portion facing forward of said rotary lawn mower cutting blade.
 2. The rotary lawn mower cutting blade of claim 1, wherein said leading cutting edge of said first cutting portion extends contiguously along said first cutting portion and said first downwardly extending end portion.
 3. The rotary lawn mower cutting blade of claim 1, wherein said leading cutting edge of said first cutting portion extends contiguously along said first cutting portion, said first downwardly extending end portion, and said first outer portion.
 4. The rotary lawn mower cutting blade of claim 1, wherein the intermediate portions are twisted so as to cause the trailing edges of said first and second cutting portions to be slightly higher than their respective leading cutting edges.
 5. The rotary lawn mower cutting blade of claim 1, wherein said cutting blade includes a center of rotation, and wherein the plane or axis of said first and second end portions are skewed causing a first edge of each of said first and second end portions to be closer to said center of rotation than a second edge of each of said first and second end portions.
 6. The rotary lawn mower cutting blade of claim 1, wherein each of said first and second outer portions has a leading cutting edge.
 7. The rotary lawn mower cutting blade of claim 1, wherein said leading cutting edge of each of said first and second inwardly extending cutting portions is beveled to define said inwardly extending leading cutting edge.
 8. The rotary lawn mower cutting blade of claim 1, wherein said center portion includes mounting means.
 9. The rotary lawn mower cutting blade of claim 1, wherein said center portion is adapted to be mounted to an external body.
 10. The rotary lawn mower cutting blade of claim 1, wherein said rotary lawn mower cutting blade is adapted to be mounted to an external body. 